1. Field of the Invention
This invention is directed to improving the properties of heavy coal fractions and, in particular, to increasing the solubility of heavy coal fractions in common organic solvents and petroleum liquids.
2. Description of the Prior Art
Processes for the liquefaction of coal and similar carbonaceous solids usually involve contacting the feed material with a hydrocarbon solvent and molecular hydrogen at elevated temperature and pressure. This results in partial breakdown of the complex high molecular weight starting material into lower molecular weight hydrocarbon liquids and gases. These are recovered from the liquefaction effluent, leaving a heavy liquefaction bottoms product which normally boils in excess of about 1000.degree. F. and generally contains suspended solid residues. The liquefaction bottoms may constitute 50% or more by weight of the total liquefaction products.
A variety of different processes for upgrading liquefaction bottoms have been proposed in the past. Exemplary of these include pyrolysis of the bottoms that produce gases, additional hydrocarbon liquids and coke, followed by steam gasification of the coke to form hydrogen and carbon monoxide for use as a fuel; see e.g., U.S. Pat. No. 4,060,478. Another process for upgrading liquefaction bottoms is disclosed in U.S. Pat. No. 4,089,772 which discloses an acid-catalyzed C-alkylation or C-acylation of liquefaction product bottoms prior to recycling the bottoms fraction to the liquefaction reaction zone.
These various processes result in more efficacious use of liquefaction bottoms. However, during subsequent coal liquefaction process, phenols present in the coal are cleaved to produce water. In liquefaction processes employing hydrogen, an excessive use of hydrogen thus occurs.
Solvent extraction of coal also leaves behind a high molecular weight, insoluble fraction of coal called coal solubilization bottoms. Like liquefaction bottoms, this heavy fraction is also the object of various upgrading processes in order to obtain increased liquid yields.